1. Field of the Invention
The present invention relates to an etchant suitable for wet-etching the solid surface, a method of etching constituent members of a device by using the etchant to manufacture the device, particularly, a method of manufacturing a device whose constituent members are made of silicon, a detergent suitable for cleaning the solid surface, and a method of cleaning constituent members of an apparatus by using the detergent and manufacturing the apparatus.
2. Description of the Prior Art
Hitherto, a mixed solution of hydrofluoric acid, nitric acid and acetic acid has been employed as an etchant or detergent. Such a mixed solution is widely used, in particular, in the process of etching single crystal silicon (hereinafter referred to as c-Si), polycrystal silicon (hereinafter referred to as p-Si), amorphous silicon (hereinafter referred to as a-Si) or the like which are used with manufacture of devices represented by electronic devices such as semiconductor devices, in the process of cleaning the surfaces of constituent members of an apparatus, such as plate members and stainless pipes, during manufacture of the apparatus, as well as in the process of cleaning appliances for us with the above process.
In those processes of using the conventional etchant or detergent to etch the surfaces of constituent members of an electronic device or the like during manufacture thereof, to clean the surfaces of constituent members of an apparatus, such as plate members and stainless pipes, during manufacture of the apparatus, and to clean appliances for use with the above process, however, nitric acid decomposes during the process and a toxic nitrogen oxide (NOx) generates. A special treatment apparatus has, therefore, been essential to prevent the generated toxic gas from giving a detrimental effect on environments.
A reaction occurred when using the conventional etchant on the surface of silicon which is a member constituting semiconductor devices as representative devices, is expressed as follows. It is seen from the reaction formula that a toxic nitrogen oxide (NO) generates. EQU 3Si+4HNO.sub.3 +18HF.fwdarw.3H.sub.2 SiF.sub.6 +4NO.uparw.+8H.sub.2 O(1)
Another problem was in that because gas generates during the process, the conventional etchant could not be applied to forming of fine patterns when semiconductor devices are manufactured through etching.
Also, in the process using a solution containing nitric acid, there usually accompanies strong heating, thus making it quite difficult to precisely control temperature at the reaction surface . s point not only has disabled application of the conventional etchant to fine etching, but also has required equipment sufficiently considered from the standpoint of ensuring safety in the processes of using the conventional etchant or detergent to etch the surfaces of constituent members of an electronic device during manufacture thereof, to clean the surfaces of constituent members of an apparatus, such as plate members and stainless pipes, during manufacture of the apparatus, and to clean appliances for use with the above process.
Because nitric acid has a property to penetrate tubes made of perfluoroalkoxy fluoride-contained polymers (PFA) which are popularly used with chemicals piping systems, it is required to employ special tubes of double- or triple-walled structure. This has been a great impediment from the viewpoint of operating control for a production factory due to the increased cost of pipings and the necessity of checking a liquid leakage at all times.
Furthermore, acetic acid used in the aforesaid mixed solution for the purpose of preventing release of nitric acid is an organic acid. Special drain treatment has thus been needed when the mixed solution is discarded, so that a COD value of the waste water is held within a predetermined level.
In the manufacture process of semiconductor devices using the conventional etchant, a sufficient etching speed could not be obtained unless concentrations of hydrofluoric acid and nitric acid used were high. For example, in order to achieve an etch rate of 1,500 angstroms per minute as an etching speed of a-Si at room temperature during manufacture of semiconductor devices, concentrations of hydrofluoric acid and nitric acid had to be set to 0.52 mol/l and 6.4 mol/l , respectively. The use of the conventional etchant which contains nitric acid of such a high concentration caused degeneration of a photoresist and, as shown in FIG. 2, deterioration in adhesion between a photoresist 3 and silicon 2 to be treated. Consequently, also as shown in FIG. 2, the amount of side etching was so increased that fine patterns could not be achieved.
Moreover, the conventional etchant used in the manufacture process of semiconductor devices contains acetic acid as one ingredient, as mentioned above. As shown in FIG. 3, however, acetic acid acts to damage the photoresist 3 such that photoresist dissolved portions 4 are produced to change the photoresist 3 into a porous film. This also has impeded the conventional etchant from being applied to forming of fine patterns.
Additionally, Japanese Patent Laid-Open No. 137472 discloses the so-called iodine etchant in which iodine is added to the conventional mixed solution of hydrofluoric acid, nitric acid and acetic acid, aiming to increase an etch rate. But this iodine etchant still requires nitric acid of a high concentration. In order to achieve the aforesaid etch rate of a-Si at room temperature, concentrations of hydrofluoric acid and nitric acid has to be set to 0.52 mol/l and 1.6 mol/l , respectively, even with iodine of 0.015 mol/l added. Thus, the problems attributable to nitric acid of a high concentration have not yet solved. Further, as shown in FIG. 4, iodine is tends to sublimate and easily escape out of the system if it is open to air. Therefore, stability of the etchant is poor to such an extent that the etch rate is lowered down 25% in 10 hours, resulting in a severe problem from the standpoint of operating control.